docs: def find_disulfide_bridges(self, threshold=3.0):
          """Run Biopython's search_ss_bonds to find potential disulfide bridges for each chain and store in ChainProp.
  
          Will add a list of tuple pairs into the annotations field, looks like this::
  
              [ ((' ', 79, ' '), (' ', 110, ' ')),
                ((' ', 174, ' '), (' ', 180, ' ')),
                ((' ', 369, ' '), (' ', 377, ' '))]
  
          Where each pair is a pair of cysteine residues close together in space.
  
          """
  
          if self.structure:
              parsed = self.structure
          else:
              parsed = self.parse_structure()
  
          if not parsed:
              log.error('{}: unable to open structure to find S-S bridges'.format(self.id))
              return
  
          disulfide_bridges = ssbio.protein.structure.properties.residues.search_ss_bonds(parsed.first_model,
                                                                                          threshold=threshold)
          if not disulfide_bridges:
              log.debug('{}: no disulfide bridges found'.format(self.id))
  
          for chain, bridges in disulfide_bridges.items():
              self.chains.get_by_id(chain).seq_record.annotations['SSBOND-biopython'] = disulfide_bridges[chain]
              log.debug('{}: found {} disulfide bridges'.format(chain, len(bridges)))
              log.debug('{}: stored disulfide bridges in the chain\'s seq_record letter_annotations'.format(chain))